Tomoji Kawai
ISIR-Sanken, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
I will talk on the topics of "DNA nanotechnology" which have been performed in our research group. @The topics include,
1. Ultra-high resolution "Scanning Probe Microscopy" imaging of single stranded and double stranded helix of DNA toward the Bio-nanotechnology.
2. Self-assembled two dimensional networks of DNA wires, nano-particle modification for nanoscale memories and DNA-FET devices toward DNA electronics and DNA based electrochemical bio-sensors.
DNA is one of the most promising molecules as the scaffold for molecular nanotechnology toward nanoelectronics. DNA has the special double helix structure with ƒÎ-electron cores of well-stacking bases for one-dimensional charge transport. The investigations of DNA on the nanostructure, electrical conductivity and electronic states have significant implications for the application of DNA in electronic devices and in DNA-based electrochemical biosensors.
It is worthily noted that divergent and controversial conclusions were reported in DNA-mediated charge transport. The direct measurements of the intrinsic electrical characteristics of polynucleotides using a conducting probe atomic force microscope have been performed using self-assembled two dimensional DNA networks. It has been revealed that DNA without carrier doping is a wide-gap semiconductor. Upon carrier doping, poly(dG)¥poly(dC) show the p-type behaviors, presumably due to the shallow ionization potentials of DNA bases. The conductivity of these molecules has been successfully controlled by chemical doping, electric field doping and photo-doping. It is found that the poly(dG)¥poly(dC) has the best conductivity and can act as a conducting nanowire. The conductive mechanism is discussed by the charge hopping model based on the SPM observation of DNA nanostructure.
For the advanced construction of DNA based molecular memories and circuits, gold and cobalt particles have been assembled within the two-dimensional DNA networks. Gold particles are arranged artificially with DNA molecular template as an average separation distance of 260nm. The pattern of the complex is controlled by changing the concentration of the DNA solution, suggesting that this method is effective in achieving the positional control of nano-scale molecular memories and circuits.
(references) T.Kawai et al; Appl.Phys.Lett.,77,3848(2000), Appl.Phys.Lett., 77,3105(2000), Surf.Sci.Lett,432,L611(1999), J.Vac.Sci.Technol.B17,1313(1999), Jpn.J.Appl.Phys. 39, 581(2000), 38,L606(1999), 38,L1211(1999)